The 2020 population forecast for the city of The Rock City in Illinois is 277. The city is growing slowly and has seen its population decline by -0.72% per year since the 2010 census. Median rent is $725 and the median house value is $99,100. The median age of the population of Rock City is 33.3 years, with males being slightly older than females. For a complete demographic breakdown of The Rock City, visit the US Census Bureau's website.